1. Field of the Invention
The present invention relates to a nitride semiconductor light emitting device and a method of manufacturing the same.
2. Description of Related Art
Recently, researches for semiconductor light emitting devices using gallium nitride (GaN) are being actively conducted in the field of conventional nitride semiconductors.
In a conventional nitride semiconductor light emitting device, differences in a lattice constant and a coefficient of thermal expansion may occur between a sapphire substrate and GaN layers grown on the sapphire substrate, so that crystal defect is caused. Therefore, in order to prevent the crystal defect from being caused, a GaN buffer layer is grown on the sapphire substrate at the lower temperature condition and the GaN layers are grown on the buffer layer at the high temperature condition. This is for reducing a difference in the lattice constant between the sapphire substrate and the GaN layers.
In the conventional nitride semiconductor, in order to grow dislocation free GaN layers on the buffer layer, a lateral epitaxial overgrowth (LEO) method or a pendeo-epitaxy method is used. In the above two methods, the GaN layers are grown from side to side to prevent the defect formed in the interface between the sapphire substrate and the GaN layers from moving to an upper layer.
FIGS. 1A to 1D illustrate a method of growing the GaN layers using the conventional LEO method.
In the LEO method, as illustrated in FIG. 1A, after primarily growing a GaN epitaxial layer 11 on the top surface of a sapphire substrate 10, as illustrated in FIG. 1B, masks 12 having a predetermined pattern are formed on the top surface of the primarily grown epitaxial layer 11, wherein the masks 12 are made of a silicon oxide layer or a silicon nitride layer.
Then, as illustrated in FIG. 1C, GaN layers 13 are re-grown in the parts where the masks 12 are not formed. At this time, the GaN layers 13 are grown on the masks 12 from side to side as illustrated in FIG. 1C by arrows. When the from side to side growth of the GaN layers 13 is completed, as illustrated in FIG. 1D, the growth of the GaN layers 13 is completed.
On the other hand, in the conventional pendeo-epitaxy method, an etching process of forming a mask to remove the GaN epitaxial layer on which the mask is not formed is added to the LEO method illustrated in FIGS. 1A to 1D. In the GaN layer formed by the LEO method or the pendeo-epitaxy method, the transmission of dislocation is commonly reduced.
As illustrated in FIG. 2, in the part where the primarily grown epitaxial layer 11 is exposed, the dislocation A that exists below is transmitted to the GaN layers 13 re-grown later. However, since the growth is performed from side to side in the parts covered with the masks 12, no dislocation is transmitted from below so that defect is reduced.
However, when the GaN layers are grown by the conventional method, the dislocation A of the part that is not covered with the mask is transmitted to above and dislocation B of high density is generated in the adhesion surface where the GaN layers 13 re-grown from side to side meet each other.
Also, according to the conventional art, defect is generated by stress formed between the masks 12 and the re-grown GaN layers 13. The electrical and optical characteristics of the nitride semiconductor and yield deteriorate by the defect such as dislocation.
Also, in the conventional LEO method or the pendeo-epitaxy method, since a process of creating the masks is used, manufacturing expenses increase. Also, since a pattern work and a re-growing process are added after primarily growing the GaN epitaxial layer, manufacturing processes are complicated.
As described above, according to the conventional art, although the LEO method or the pendeo-epitaxy method is used in order to reduce the defect caused by lattice mismatching, it is not possible to remarkably reduce the defect such as the dislocation. Also, the processes become complicated due to the addition of processes and the manufacturing expenses increase. Therefore, it is required to provide a gallium nitride (GaN) semiconductor light emitting device having excellent electrical and optical characteristics in which it is possible to prevent the defect such as the dislocation from being generated by the lattice mismatching between the sapphire substrate and the nitride semiconductor material such as GaN and a method of manufacturing the same.